Make TakeUntil obey Rx contract
Ignore furthur messages after entering terminate state
OperatorScan should check for MAX_VALUE on request
Fix the bug that Switch doesn't propagate 'unsubscribe'
Merge pull request #1667 from zsxwing/fix-switch

Fix the bug that Switch doesn't propagate 'unsubscribe'
Merge pull request #1659 from davidmoten/scan-fix

OperatorScan should check for MAX_VALUE on request
Merge pull request #1657 from zsxwing/fix-onErrorReturn

Ignore furthur messages after entering terminate state
Error Handling Unsubscribe and Terminal State
Merge pull request #1669 from benjchristensen/unsubscribe-in-error-handlers

Error Handling Unsubscribe and Terminal State
Merge pull request #1656 from zsxwing/fix-takeUntil

Make TakeUntil obey Rx contract